Saint Leo the Great on the incarnation.
From Universalis: Office of Readings:
"Thus the Son of God enters this lowly world. He comes down from the throne of heaven, yet does not separate himself from the Father’s glory. He is born in a new condition, by a new birth.
He was born in a new condition, for, invisible in his own nature, he became visible in ours. Beyond our grasp, he chose to come within our grasp. Existing before time began, he began to exist at a moment in time. Lord of the universe, he hid his infinite glory and took the nature of a servant. Incapable of suffering as God, he did not refuse to be a man, capable of suffering. Immortal, he chose to be subject to the laws of death.
He who is true God is also true man. There is no falsehood in this unity as long as the lowliness of man and the pre-eminence of God coexist in mutual relationship.
As God does not change by his condescension, so man is not swallowed up by being exalted. Each nature exercises its own activity, in communion with the other. The Word does what is proper to the Word, the flesh fulfils what is proper to the flesh.
One nature is resplendent with miracles, the other falls victim to injuries. As the Word does not lose equality with the Father’s glory, so the flesh does not leave behind the nature of our race.
One and the same person - this must be said over and over again - is truly the Son of God and truly the son of man. He is God in virtue of the fact that in the beginning was the Word, and the Word was with God, and the Word was God. He is man in virtue of the fact that the Word was made flesh, and dwelt among us."